I'm terribly new to betta fish, and my first one used to be pretty active.
He always liked to just float around, but when I put him in his new 5gallon tank, he loved it. He was always swimming, trying to beat the current, having fun.

Well, now his fins seems to be tearing (and they look a bit black? maybe it's coloring?)
And he just seems very lethargic at the bottom of the tank. I bought him a big accessory for his tank with lots of hiding, but he just does't want part of anything.

His water is about 75-80, and I did put chemicals in it to make it betta worthy.

thank you!
yea he's in a 5gallon with a filter so i thought once a week?

Once a week after it is cycled. During the cycling period (typically the 1st 8 weeks) I would do 1 gallon every other day and 2 gallons once week (I choose a non work day for this) with gravel vacuuming on the 2 gallon day.

on the 1 gallon days, just scoop a gallon out and add a treated gallon back.

Make sur eyou also put a pinch or two of salt in his home tank also, or whatever tank you plan on leaving him in while he has torn fins. I always put salt in my tanks because it helps with electrolytes and if they get harmed in anyway it helps bettle infection/fin rot.

The only thing to note about giving salt baths, do it when you can sit and watch your betta. Some hate the excess salt so if they get too combative you need to take them out immediately! If you keep them in there too long it can also harm the fish so only do it for about five minutes